Thermocouple is often used to measuring temperature, and it is based on the metal conductor resistance value increases with the increase of the temperature of the properties for temperature measurement. And thermocouple are mostly made of pure metal materials, the application is more platinum and copper, in addition, now have begun to use the materials such as nickel, manganese and rhodium thermocouple. Thermocouple type has the following several kinds of 1, normal thermocouple: from the thermocouple temperature measurement principle, the measured the change in temperature is directly measured by thermocouple resistance change, therefore, the wires of a thermocouple body such as a variety of wire resistance change will affect temperature measurement. 2, thermocouple, thermocouple is by thermal components ( The resistor body) , wire, insulation materials, stainless steel casing combination solid body, its diameter is commonly phi - 2 Phi is 8 mm, xiaoke reaches 0. 25φmm。 Compared with ordinary thermocouple, it has the following advantages: (1) small volume, no internal air gap and thermal inertia, the measured value after small; (2) good mechanical properties, resistance to vibration and shock. (3) can bend, easy to install (4) long service life. 3, end thermocouple: end thermocouple temperature sensing element resistance wire winding by special processing, close to the face in the thermometer. Compared with general axial thermocouple, it can reflect more correctly and quickly end face of the actual temperature being measured, is suitable for measuring temperature bearing and other parts of the face. 4, flame-proof thermocouple, flame-proof thermocouple through the special structure of the junction box, its shell internal explosive mixed gas by affected by sparks or electric arc explosion limit within the junction box, that wouldn't make production field explosion. Flame-proof thermocouple can be used in the bla - B3c level zone with explosion danger place temperature measurement.